The present invention relates generally to torsion damping devices of the kind comprising two coaxial parts mounted for limited angular movement relative to one another within a predetermined sector, and elastic means interposed circumferentially between the two parts.
Torsion damping devices of this kind make it possible to achieve the regulated transmission of torque from one coaxial part to the other, and filter out the vibrations, and in particular the sound vibrations, which can occur throughout the length of the kinematic chain in which the torsion damping device is fitted.
Such devices are often fitted in clutches, and in particular in motor vehicle clutches, in the form of assemblies commonly referred to as clutch plate assemblies with a damping hub, in which case one of their parts carries a friction disc capable of being clamped between two elements integral in rotation with a first shaft, which in practice in a driving shaft, whilst the other part is rotationally fixed to a second shaft, which in practice is a driven shaft.
It is known to insert, between the two coaxial parts of such a torsion damping device, friction means which introduce a hysteresis effect into the operational characteristics of the device; as is known, this hysteresis effect results in a difference, for the same angle of movement between the parts, between the value of the torque transmitted between these parts during a first direction of movement, which is commonly referred to as the positive direction and corresponds to the drive condition of the whole arrangement, and the value of this torque transmitted during the opposite direction of movement, which is commonly referred to as the overrun direction and corresponds to the overrun condition of the arrangement.
In fact, it is shown that, for certain applications, this hysteresis effect makes a contribution towards limiting the vibrations and the noise emitted by all the rotating members in the kinematic chain to which the driving and driven shafts in question belong.
In practice, the friction means employed for this purpose generally comprise at least one friction washer, which is axially interposed between the two rotatable parts, the said friction washer being in contact with one of these parts whilst being capable of being rendered integral in rotation with the other part for at least a portion of the sector of angular movement between these parts, and which is subjected to an axial elastic clamping force.
An arrangement of this kind is described in French Patent Application No. 76/34242 filed on Nov. 15, 1976 and published under No. 2,370,902.
This French patent application proposes, amongst various possible embodiments, to produce the axial elastic clamping force by means of a clamping disc provided with elastically deformable, radially projecting lugs.
However, in this patent application, which moreover relates to a very particular arrangement, the radial lugs on this clamping disc extend from the external periphery of the disc, in order to bear axially on the short posts joining together the guide discs which customarily constitute one of the rotatable coaxial parts in question.
As a result, in this embodiment, it is the clamping disc itself which acts axially on the friction washer associated therewith.
Although this arrangement has proved and continues to prove satisfactory, it exhibits various disadvantages.
First of all, if no play is allowed for its lugs in a direction at right angles to the posts, the clamping disc is to some extent restricted by the lugs and its axial elasticity is thereby limited. Now, in practice, this play is not easily compatible with the axial clamping which the posts in question must provide. Moreover, the number of radial lugs which this clamping disc can incorporate is dependent on the number of posts, and this can prove inadequate for obtaining the desired clamping force.
The object of the present invention is to provide a torsion damping device having an elastic clamping disc which does not exhibit these disadvantages.